1. Field of the Invention
The present invention relates to an apparatus and a method for performing image processing on image data acquired by a digital camera or the like.
2. Description of the Related Art
The digital camera has a function of automatically controlling final image quality in terms of white balance, contrast, color, etc. In the automatic white balance adjustment, a color temperature of a light source illuminating an object is estimated from image-taking conditions and image data of the object, and the color of the light source is cancelled to gray such that a resultant adjusted image has natural high quality. In the automatic brightness (contrast) adjustment, the brightness and the tone of the luminance components are automatically adjusted, while in the automatic color adjustment, the saturation and the hue of the color components are automatically adjusted. These adjustments may be performed depending on a scene type (such as a daytime scene, an evening scene, a portrait, etc.) inferred from the image-taking conditions and the taken image data such that the image has brightness and color representation optimized depending on the inferred scene type.
In the automatic adjustment process described above, a slight change in image-taking condition or a slight movement or a change in an object may occur between cuts, and such a change may result in a slight change in detected color temperature or other automatically detected parameters, which may in turn result in a slight change in the automatically adjusted image quality. Even such a slight change may result in incorrect inference about the scene type, which may cause the image processing to be performed according to improper conditions determined from the incorrect scene type. This may result in a difference in image quality between cuts, which may produce an artifact. A method of preventing the above problem is to determine a correlation between cuts by comparing image-taking conditions and the image data between the cuts. If the correlation is high, the inferred scene type is inherited from the previous cut. Note that the term “previous cut” is used in the present description to express a cut of an image taken in the past time. This method makes it possible to minimize the change in image quality between the cuts. Japanese Patent Laid-Open No. 2000-165891 discloses a technique to minimize a change in the white balance.
To determine a correlation between the current cut and the previous cut in common for the white balance adjustment process, the luminance adjustment process, and the color adjustment process, the similarity between the cuts may be determined in common for the three adjustment processes, and the correlation in each process may be judged using the determined similarity. The similarity may be calculated from changes between cuts in terms of aperture value Av, shutter speed Tv, ISO sensitivity, face detection, luminance histogram shape, and color temperature. However, this method of determining the correlation based on the similarity determined in common may cause following problems. For example, in an outdoor scene such as that shown in FIG. 6 in which images of two airplanes are taken as main objects, if the two airplanes are different in color, the correlation based on the similarity is low although two successive cuts are equal in color temperature of a light source and brightness. As a result, conditions in terms of white balance, contrast, and the like are not inherited from the previous cut, and thus a change can occur in white balance and brightness between cuts.
Thus, there is a need for a technique to properly reduce differences between cuts in the white balance adjustment process, the contrast adjustment process, and the color adjustment process.